Dry deposition of aerosols onto forest

Abstract

Recent knowledge of the dry deposition of aerosols onto forests, focusing especially on field measurements in East Asia, is summarized with respect to aerosol impact on the vegetation in the region. Direct measurements of aerosol deposition in Japan by means of the gradient method and the relaxed eddy accumulation method were introduced together with their principles. They indicate that the levels of deposition velocity of PM2.5 sulfate were in agreement with experimental results in North America and Europe and were higher than those calculated by theoretical models. The deposition velocity was probably influenced by humidity due to the growth in size of hygroscopic aerosols. The calculations taking into account the effect of growth of hygroscopic aerosols were in reasonable agreement with the measurements. A complex terrain contributed to increasing the range of measured deposition velocities. However, the measurements agreed with calculated deposition velocities on average for about 2 weeks. Measurements of vertical profiles of PM2.5 components in a forest indicate that the dry deposition of NH4NO3 particles was more efficient than that of (NH4)2SO4 particles, probably due to the volatilization processes of NH4NO3. Finally, a case study on the dry deposition of elemental carbon estimated by the inference method in a tropical forest in Thailand was introduced.